mlxsw: spectrum: Use FID instead of vFID to setup flooding

Use a FID index instead of vFID and ease the transition towards a
generic FID struct.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>